What is Déjà vu?

Hey, Vsauce. Michael here. And today we're going to discuss déjà vu. What is it, and

why does it occur? You know, those moments where the current situation feels like it's

happened before? You're certain it has, but you don't know when, or how it became so familiar.

It's difficult to scientifically study déjà vu because there's no reliable way to cause

it to happen in people's heads in a laboratory.

But here's what we do know: humans don't seem to experience déjà vu until they're at least

8 or 9 years old. It's most frequent in your teens and twenties, and then tapers off as

you get older. So, it might have something to do with brain development. In fact, we

should probably go get ourselves a brain. That was easy. Now, like a stomach ache, déjà

vu may be a symptom with many possible causes. A lot of the popular theories about what causes

it involve a disconnect that may be occurring between the deep structures of the brain that

process our experiences unconsciously, and the parts of the brain that are conscious

of what they experience, process it, and then tell us what we're seeing.

For the sake of simplicity, let's begin with the visual system. Now, the brain sits in

your head like this, and your eyeballs are over here seeing things, sending that signal

to the back of the brain, the Occipital lobe, where visual cortex is. That's where the image